In the drilling of oil and gas wells, it is common to install a steel pipe or casing within the open wellbore in order to provide stability to the walls of the wellbore passing through the formation and to isolate and seal off formation fluid zones from one another. Typically, the casing is cemented in place in order to bond the casing to the wall of the wellbore. More specifically, a casing string is inserted into a wellbore filled with drilling mud. Once the casing string is positioned in the wellbore, a cementing head is secured to the top of the casing string. The cementing head includes a valve system for injecting and removing fluids during the cementing process and a receptacle(s) or chamber(s) in which at least two plugs are carried. During the cementing process, a first plug, dart, ball or similar device, often referred to as a “bottom plug” is released into the casing string. The first plug is pumped down the casing string by a cement slurry until the first plug seats at a desired location within the casing string (often in proximity to the end of the casing string). As the first plug moves down the casing string, the first plug functions to wipe the casing string of residual mud. In addition, the first plug forms a barrier between the mud in the wellbore below the first plug and cement slurry in the casing string above the first plug. Once the desired amount of cement slurry is pumped into the casing string, a second plug is released at the top of the cement slurry column, thus functioning as a barrier at the top of the cement slurry column. Various types of displacement fluids may be used to apply pressure to the second plug to drive it down the casing string. In so doing, the cement slurry is forced out into the annulus formed between the casing string and the walls of the wellbore, either through ports formed in the casing or through a port in the first plug. As the cement slurry is forced into the annulus, formation fluids and mud contained in the annulus are forced out of the wellbore and recovered at the top of the casing string. After the cementing job is complete, the cementing head if flushed to remove any remaining cement slurry.